MXPA01010871A

MXPA01010871A - Low water peak optical waveguide fiber and method of manufacturing same.

Info

Publication number: MXPA01010871A
Application number: MXPA01010871A
Authority: MX
Inventors: Daniel W Hawtof
Original assignee: Corning Inc
Priority date: 1999-04-26
Filing date: 2000-04-07
Publication date: 2002-05-06
Also published as: ATE316944T1; DE60025823T2; WO2000064825A1; US6477305B1; JP4596442B2; AU4973100A; CA2371249A1; BR0009970A; CN1235820C; EP1181254B1; EP1181254A1; JP2002543026A; KR20020012547A; DE60025823D1; CN1348431A

Abstract

A cylindrical glass body having a low water content centerline region and method of manufacturing such a cylindrical glass body for use in the manufacture of optical waveguide fiber is disclosed. The centerline region of the cylindrical glass body has a water content sufficiently low such that an optical waveguide fiber made from the cylindrical glass body of the present invention exhibits an optical attenuation of less than about 0.35 dB/km, and preferably less than about 0.31 dB/km at a measured wavelength of 1380nm. A low water content plug (46, 54) used in the manufacture of such a cylindrical glass body, an optical waveguide fiber having a low water peak, and an optical fiber communication system incorporating such an optical waveguide fiber is also disclosed.

Description

FIBER OPTIC WAVE GUIDE OF LOW PICO WATER AND METHOD TO MANUFACTURE THE SAME RELATED REQUEST This application claims the benefit of the priority date of the provisional patent application of E.U.A No. 60/131, 033 issued April 26, 1999, entitled "Low Water Peak Optical Waveguide and Method of Making Same".

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to the field of optical waveguide fibers, and more particularly to optical waveguide fiber preforms and methods for making the optical waveguide fiber preforms from which the optical waveguide forms are formed. Optical waveguide fibers of low water peak.

TECHNICAL BACKGROUND Generally speaking, an important objective of the telecommunications industry is to transmit large amounts of information, over long distances, in short periods. Typically, as the number of system users and frequency of system usage increases, the demand for system sources also increases. One way to combat this demand is to increase the bandwidth of the medium used to transport this information over long distances. In optical telecommunication systems, the demand for optical waveguide fibers having an increased bandwidth is particularly high. In recent years, significant advances have been made in the manufacture of optical waveguide fiber, which in turn has increased the capacity to transport useful fiber light. However, as is well known, electromagnetic radiation traveling through an optical waveguide fiber is subject to attenuation or loss due to many mechanisms. Although some of these mechanisms can not be reduced, others have been eliminated, or at least substantially reduced. A particularly problematic component of fiber optic attenuation is attenuation due to the absorption by the optical waveguide fiber of impurities present in the light-conducting region of the fiber. Particularly difficult is the attenuation caused by the hydroxyl radical (OH), which can be formed in the optical waveguide fiber when a source of hydrogen is present in the fiber material, or when the hydrogen available from many sources during the process of Fiber manufacturing diffuses in the glass. Generally speaking, hydrogen binds with the available oxygen in SiO2 and / or GeO2 and / or another oxygen-containing compound in the glass matrix to form the OH and / or OH2 bonds generally referred to as "water." The increase in attenuation due to OH or water in the glass can be as high as around 0.5 to 1.0 dB / km, the attenuation peak usually occupying the 1380 nm window. As used herein, the phrase "1380 nm window" is defined as the scale of wavelengths between about 1330 nm to about 1470 nm. The attenuation peak, generally mentioned, as the water peak, has avoided useful electromagnetic transmission in the 1380 nm window. Until now, telecommunications systems prevented the peak of water from residing in the 1380 nm window when operating in the 1310 nm window and / or the 1550 nm window, among others. With the success of wavelength division multiplexing ("WDM") and advances in amplifier technology, which allow telecommunication systems to operate over wide wavelength scales, it is now likely that all wavelengths wave between about 1380 nm and about 1650 nm will be used to transfer data in optical telecommunication systems. By removing the water peak from the optical wavelength fiber that is used with such systems, it is an important aspect to allow the operation of the system on the full scale.

BRIEF DESCRIPTION OF THE INVENTION One aspect of the present invention relates to a method for manufacturing a cylindrical glass body for use in the manufacture of optical waveguide fiber. The method includes the steps of chemically reacting at least one of the constituents of a moving fluid mixture that includes at least one glass-forming precursor compound in an oxidizing medium to form a silica-based reaction product. At least a portion of the reaction product, which includes hydrogen bound to oxygen, is collected or deposited to form a porous body. A central line hole extending axially through the porous body is formed during the deposition process, for example, by depositing the reaction product on a substrate, and thereafter removing the substrate. The porous body is dried and consolidated to form a glass preform, and the center line hole is closed under suitable conditions to make an optical fiber having an optical attenuation of less than about 0.35 dB / km at a wavelength of 1380 nm. Preferably, the fiber has an optical attenuation of less than 0.31 dB / km at a wavelength of 1380 nm.

In another aspect, the present invention relates to a cylindrical glass body for use in the manufacture of optical waveguide fiber that is made by the method described above. A further aspect of the present invention is directed to an optical waveguide fiber. The optical waveguide fiber includes a core glass containing silica, at least a portion of which includes hydrogen bound to oxygen. The silica-containing core glass further includes a center line region, at least a portion of which includes a dopant, and is formed by closing a center line hole in a preform. A coating glass surrounds the core glass containing silica such that the optical waveguide fiber exhibits an optical attenuation of less than about 0.31 dB / km at a wavelength of about 1380 nm. In still another aspect, the present invention is directed to a fiber optic communication system. The system includes a transmitter, a receiver, and an optical fiber to communicate an optical signal between the transmitter and the receiver. The optical fiber includes a core glass containing silica, at least a portion of which contains oxygen bound hydrogen, has a dopant containing a central line region formed to close the center line hole of a preform. The optical fiber further includes a coating glass surrounding the core glass containing silica. Preferably, said optical fiber has an attenuation of less than about 0.31 dB / km at a wavelength of about 1380 nm.

A further aspect of the present invention is directed to a method for manufacturing a cylindrical glass body for use in the manufacture of optical waveguide fiber. The method includes the steps of chemically reacting at least some of the constituents of a moving fluid mixture that includes at least one precursor compound that forms glass in an oxidation medium to form a silica-based reaction product. At least a portion of the reaction product, including hydrogen bound to oxygen, is collected or deposited to form a porous body. A central line hole extending axially through the porous body is formed during the deposition process, for example, by depositing the reaction product on a substrate, and thereafter removing the substrate. The porous body is dried and consolidated to form a glass preform having a central line hole, which is subsequently closed. The steps of drying, consolidating and closing are performed under suitable conditions to result in a solid glass body including a centerline region having an average weight-average OH content of less than about 1 ppb. A further aspect of the present invention relates to a shutter that is used to seal the orifice of the centerline of a soot preform used to manufacture optical waveguide fiber. The silica-containing glass obturator has an OH content of less than about 5 ppm by weight and preferably is chemically dried so that it has an OH content of less than 1 ppb by weight.

The method of the present invention results in a number of advantages over other methods known in the art. Conventionally, optical waveguide fiber preforms made by an external vapor deposition process (OVD) are consolidated in a chlorine-containing atmosphere to chemically dry the preform and thus form a consolidated glass preform having a pre-formed orifice. central line that extends axially between them. The core glass preform is typically placed inside a rewind oven and heated to a temperature sufficient to facilitate rewinding or stretching of the core preform in a small diameter cylindrical glass body or core shank. During the rewind operation, the centerline hole of the core preform is closed by, for example, applying vacuum (eg, pressure of about 200 mTORR or less) along the hole in the centerline. The reduction in pressure within the center line hole ensures a complete closure of the center line hole so that the core shank has a solid central line region extending axially therethrough. After the rewinding step, the resulting core shank is typically overcoated with a layer of coating soot, by depositing a coating soot, for example by means of an OVD process. Once covered with sufficient coating soot, the core rod overcoated with the resulting soot is chemically dried and consolidated to form an optical fiber preform that can thereafter be stretched on an optical waveguide fiber. Despite chemical drying and consolidation steps, it has been found that such optical waveguide fibers exhibit a relatively high level of attenuation measured at approximately 1380 nm. Since the telecommunication systems currently in use do not operate at or in the immediate vicinity of 1380 nm, this defect has been much recognized. However, with recent advances made in WDM, amplifier technology, and laser sources, eliminating the water peak measured at 1380 nm has become a priority. The water peak is a result of water being trapped in the glass during the fiber manufacturing process. In the case of the OVD process, it is believed that a large portion of water is trapped within the core line region of the core rod prior to or during closure of the center line hole. Although some preforms are chemically dried and agglutinate during consolidation, it was found that the region of the glass surrounding and defining the centerline orifice is re humidified after drying. More commonly, said rehumidification occurs through the physisorption of water (OH2) and / or water chemisorption (Beta OH) at the time of exposure of the centerline orifice to an atmosphere that includes a hydrogen-containing compound, such as, but not limited to water (H2O) after consolidation. A major advantage of the method of the present invention is that it greatly reduces the amount of water trapped within the core line region of the core shaft. Also, the optical waveguide fiber made from said core rod shows a much lower water peak at 1380nm, and in the 1380nm window as a whole, and therefore has a lower optical attenuation in the 1380 nm window than optical waveguide fiber manufactured in accordance with standard methods from preforms manufactured by the OVD process. An additional advantage of the method and the cylindrical glass body of the present invention is that the optical waveguide fiber made from said cylindrical glass bodies can now be operated at any selected wavelength on a wavelength scale of about 1300 nm to about 1680 nm without an undone optical attenuation. More specifically, said fibers exhibit less than about 0.35 dB / km, and preferably less than about 0.31 dB / km at each wavelength within a wavelength range from about 1300 nm to about 1680 nm. In addition, the method of the present invention is also economical to practice and can be practiced without the production of additional non-environmentally friendly waste products. Further features and advantages of the invention will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from the description or will be recognized by practice of the invention as described herein., including the detailed description that follows, the claims, as well as the accompanying drawings. It will be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or structure for the understanding of the invention. nature and character of the invention as it is claimed. The accompanying drawings are included to provide further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a cylindrical glass body showing the central line region R2 in accordance with the present invention. Figure 2 is a schematic view illustrating the fabrication of a porous body using an exterior vapor deposition process in accordance with the present invention. Figure 3 is a cross-sectional view of the porous body of Figure 2 shown suspended within a consolidation furnace. Figure 4 is a cross-sectional view of the porous body of Figure 2 shown suspended within a consolidation furnace according to the first preferred embodiment of the present invention.

Fig. 5A is a cross-sectional view of the porous body of Fig. 2 shown adapted with an upper shutter and suspended within a consolidation furnace according to the first preferred embodiment of the present invention. Figure 5B is an enlarged cross-sectional view of an upper shutter shown to be placed inside the handle as shown in Figure 5A. Figure 6A is a cross-sectional view of the porous body of Figure 2 shown adapted with a cutting member and suspended within a consolidation furnace according to the first preferred embodiment of the present invention. Figure 6B is an elongated cross-sectional view of the cutting element shown positioned within the sleeve as shown in Figure 6A. Figure 7A is a cross-sectional view of a concreted glass preform resulting from the consolidation of the porous body shown in Figure 4 which is shown stretched in a reduced diameter core shank. Figure 7B is a cross-sectional view of a concreted glass preform resulting from the consolidation of the porous body shown in Figure 5 which is shown stretched on a reduced diameter core shank.

Figure 7C is a cross-sectional view of a concreted glass preform resulting from the consolidation of the porous body shown in Figure 6A which is shown stretched in a reduced diameter core shank. Figure 7D is an enlarged cross-sectional view showing the plunger cutting and operating element as shown in Figure 7C. Fig. 8 is a cross-sectional view of a concreted glass preform that is shown positioned within a rewind oven according to the second preferred embodiment of the method of the present invention. Figure 9 is a cross-sectional view of a concreted glass preform which is shown placed in a rewinding oven in accordance with the second preferred embodiment of the method of the present invention. Figure 10 is a plane of spectral attenuation of an optical waveguide fiber of the present invention. Figure 11 is an optical fiber communication system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Reference is now made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers will be used in all the drawings to mention the same or similar parts. An exemplary embodiment of the cylindrical glass body of the present invention is shown in Figure 1, and is generally designated throughout the document by reference numeral 20. In accordance with the invention, a cylindrical glass body 20 includes a glass region containing silica 22, at least a portion of which includes hydrogen bound to oxygen. The silica-containing glass region 22 includes a central line region 24 that has a weight average OH content of less than 2 ppb, and preferably less than about 1 ppb. The central line region 24 joins a smaller diameter (preferably germania) impurifier containing the region 26 (shown by a radial distance R-i), and both central line regions 24 and the confounding region 26 that extends longitudinally along the central axis 28 of the cylindrical glass body 20. The central line region 24, represented by the radial distance R2 as shown in FIG. Figure 1 is defined as that portion of the glass body 20 where about 99% of the propagated light travels. As stated differently, when the attenuation spectrum of an optical waveguide fiber fabricated by a glass body 20 is measured in a Photon-Kinetics attenuation measuring bank (PK bank) at a wavelength At 1380 nm, the optical attenuation measures less than about 0.35 dB / km and more preferably less than about 0.31 dB / KM. According to the invention, the cylindrical glass body 20 is preferably formed by the chemical reaction of at least some of the constituents of a moving fluid mixture that includes at least one precursor compound that forms glass in a medium to oxidize to form a reaction product based on silica. At least a portion of this reaction product is directed towards a substrate, to form a porous body, at least a portion of which includes hydrogen bound to oxygen. The porous body can be formed, for example, by depositing layers of soot on a bait rod by means of an OVD method. Said OVD procedure is illustrated in Figure 2. As shown in Figure 2, a bait rod or mandrel 30 is inserted through a tubular sleeve 32 and mounted on a lathe (not shown). The lathe is designed to rotate and move the mandrel 30 in close proximity to a soot-generating burner 34. As the mandrel 30 is rotated and translated, the reaction product is based on silica 36, generally known as soot , it is directed towards the mandrel 30. At least a portion of the silica-based reaction product 36 is placed in the mandrel 30 in a portion of the sleeve 32 to form a porous body 38 therein. Although this aspect of the present invention has been described in conjunction with a mandrel 30 that is crossed by a lathe, it will be understood by those skilled in the art that the soot generating burner 34 may be crossed in place of the mandrel 30. In addition, this aspect of The present invention is not intended to limit the deposition of soot to an OVD process. In contrast, other methods for chemically reacting at least some of the constituents of a moving fluid mixture, such as, but not limited to, supplying liquid of at least one precursor compound that forms glass in a medium to oxidize, they can be used to form the silica-based reaction product of the present invention, as described, for example, in U.S. Provisional Patent Application serial number 60 / 095,736, filed August 7, 1997, and PCT application serial number PCT / US98 / 25608, filed on December 3, 1998, the contents of which are incorporated herein by reference. In addition, other methods, such as the internal vapor deposition (IV) process, and the modified chemical vapor deposition (MCVD) process, also apply to the present invention. Once the desired amount of soot has been deposited on the mandrel 30, the deposition of the soot is terminated and the mandrel 30 is removed from the porous body 38. In accordance with the present invention and as shown in Fig. 3, At the time of removing the mandrel 30, the porous body 38 defines a central line hole 40 which passes axially therethrough. Preferably, the porous body 38 is suspended by the sleeve 32 in a down feed sleeve 42 and is placed inside a consolidating furnace 44. The end of the center line hole 40 remote from the sleeve 32 is preferably adapted with a lower plug 46 before placing the porous body 38 inside the consolidation furnace 44. The porous body 38 is preferably dried chemically, for example, by exposing the porous body 38 to an atmosphere containing chlorine at elevated temperature within a consolidating furnace 44. The chlorine-containing atmosphere 48 effectively removes water and other impurities from the porous body 38, which would otherwise have a undesirable effect on the properties of the optical waveguide fiber manufactured by the porous body 38. In a porous body formed by OVD 38 the chlorine flows sufficiently through the soot to effectively dry the total preform, including the region surrounding the centerline orifice 40. After the chemical drying step, the temperature of the oven is raised to a temperature sufficient to consolidate the soot preform into a concreted glass preform, preferably about 1500 ° C. According to the method of the present invention, the center line orifice 40 is closed, either during or after the consolidation step, under suitable conditions to result in a solid concreted glass body that can also be processed to form a fiber. Optical waveguide that exhibits optical attenuation less than 0.35 dB / km, and preferably less than 0.31 dB / km at a wavelength of 1380 nm. In the preferred embodiment, the central line region 24 has a weight average OH content of less than 1 ppb.

In the past, and as described above in this application, after chemical drying and consolidation, the glass preform was routinely exposed to an environment containing water, such as an ambient atmosphere, for example, when the glass preform it was removed from the consolidation furnace and moved to a rewind furnace for additional processing steps. Invariably, the optical waveguide fibers fabricated using said preforms showed excessively high levels of optical attenuation in the 1380 nm window. It has been found that this high attenuation, generally known as the "water peak", is largely due to the absorption of water by the portion of the glass preform that surrounds the center line hole before the central line hole is closed. . In fact, it has been recognized that the water-absorbed water (OH2) and the chemosorbide water (Beta OH) in the glass that attaches to the centerline orifice results in substantially instantaneous when the glass is exposed to an atmosphere containing a compound of hydrogen such as, but not limited to water (H2O). In addition, the longer the exposure time, the greater the amount of water absorbed by the glass. In this way, any exposure to the atmosphere, or any atmosphere containing a hydrogen compound, no matter how short the period, will re-humidify that portion of the glass preform that attaches to the centerline hole. This rehumidification provides the impurities that cause the water peak presented by optical waveguide fibers manufactured using standard fiber manufacturing processing techniques of preforms formed by an OVD process. In accordance with the method of the present invention, closing the center line orifice under conditions suitable to result in a solid glass body that can be used to make an optical waveguide fiber having an optical attenuation of less than 0.31 dB / ka a wavelength of 1380 nm can be provided in a number of ways. In a first embodiment of the method of the present invention, exposure of the centerline orifice to an atmosphere containing a hydrogen compound is avoided by following the steps of chemically drying and consolidating the porous body. According to this embodiment, the center line hole does not have an opportunity to re-humidify before closing the center line hole. In a second embodiment of the method of the present invention, the water contained within the portion of the concreted glass preform surrounding the centerline hole as a result of post-consolidation rehumidification is chemically removed from the glass prior to closure of the orifice. of central line, preferably in rewind. According to the first preferred embodiment of the method of the present invention, the rehumidification of the glass joining the centerline orifice can be significantly reduced or avoided by closing the center line hole during consolidation. As illustrated in FIG. 4, the end of the center line hole 40 away from the sleeve 32 fits with a glass shutter 46 prior to the consolidation step. After drying with chlorine, the porous body 38 is driven down into the hot zone (not shown) of the consolidation furnace 44, preferably in an atmosphere of inert gas 50, such as helium. The elevated temperature preferably of about 1500 ° C, generated in the hot zone, concretes the porous body 38 as it enters the hot zone. The inwardly directed concreted forces reduce the diameter of the porous body 38 thus closing the porous body 38 in the plug 46 to effectively seal one end of the center line hole 40. The porous body 38 is also driven downward to make up the rest of the body porous 38 thus forming a concreted glass preform having a central line hole 40 sealed at its sealed ends. After the consolidation step, the concreted glass preform is preferably removed from the hot zone and the center line hole 40 is exposed to a vacuum of at least 10 Torr, more preferably 100 mTorr, through an inner sleeve 52, which communicates with the orifice of central line 40 through a sleeve 32. The concreted glass preform is pushed back down into the hot zone of the consolidation furnace 44 while the center line hole 40 is under vacuum. As the concreted glass preform enters the hot zone, it is sufficiently softened so that the vacuum force acting on the glass joining the center line hole 40 stretches the glass inwardly, thus closing the line orifice. 40 as the concreted glass preform continues to move through the hot zone. The resulting solid concreted glass preform can then be removed from the consolidation furnace 44 and stored for further processing, or moved to a rewind oven where it can be stretched on a reduced diameter shank. In any event, since the center line hole 40 is closed (ie, the concreted glass preform has a solid centerline region), the centerline region will not be exposed to the atmosphere and thus will not become to humidify at the time of removal of the consolidation furnace 44. Alternatively, as illustrated in Figure 5A, the lower plug 46 of the top plug 54 is inserted into the opposite ends of the center line hole 40 prior to placing the porous body 38 inside the consolidation furnace 44. As shown in Figure 5B, the top plug 54 has an elongated portion 56 that is held within the sleeve 32, and a narrow portion 58, which extends into the center line hole 40. As described above, with reference to Figure 4, after chemical drying, the porous body 38 is driven down in the hot zone in the consolidation furnace 44. As the cue porous rpo 38 enters the hot zone, is progressively realized, first closing a lower shutter 46 and finally closing an upper shutter 54, thus sealing the center line hole 40. Since the sealing of the center line hole occurs during consolidation, the inert gas atmosphere 50 within the consolidation furnace 44, preferably helium, will be trapped within the sealed centerline orifice. Also, the concreted glass preform is exposed to elevated temperature for a period sufficient to diffuse the inert gas from the center line orifice 40. Diffusion is preferably carried out in a conservation oven, however diffusion can be achieved within the consolidation oven too. Diffusion of the inert gas from the center line orifice 40 reduces the pressure within the centerline orifice 40 below the pressure outside the concreted glass body, thereby forming a passive vacuum within the sealed centerline orifice 40. More preferably however, the centerline orifice 40 is vacuum-loaded through the inner sleeve 52 as shown in Figure 5A before concreting the end of the porous body 38 to the top shutter 54. In this way, the narrow portion 58 of the Upper shutter 54 is measured so that porous body 38 does not fully close in upper shutter 54 as porous body 38 is consolidated into a concreted glass preform. Conversely, after consolidation, the centerline orifice 40 is exposed to a reducing atmosphere by drawing vacuum through the lower sleeve 52 as the concreted glass preform is pushed down into the hot zone of the oven. consolidation 44. The elongate portion 56 of the top plug 54 is formed so that the inert gas within the center line hole 40 can pass through the elongate portion 56 of the top plug 54 as the vacuum is pushed. As the atmosphere within the center line hole 40 is further reduced, the hot concreted glass is pushed into engagement with a narrow portion 58 of the top plug 54, thereby sealing the center line hole 40. Since the inert gas has been removed from the center line hole 40 by active vacuum, this embodiment of the present invention avoids the diffusion step and thus reduces the total processing time. In a preferred embodiment, the glass shutter 46 is placed in the center line hole 40 at the end of the porous leather 38 remote from the sleeve 32, and a hollow tubular glass element or cutting element 60 having an open end that looks the plug 46 is positioned in the center line hole 40 opposite the plug 46 as shown in Figure 6A. As described above with respect to Figure 5A, after drying with chlorine, the porous body 40 is driven down into the hot zone of the consolidation furnace 44 to seal the center line hole 40 and consolidate the porous body 38 in a concreted glass preform. This can be done by sealing both the upper and lower part of the center line hole 40 with a porous body passage 38 through the hot zone followed by the diffusion of the inert gas from the center line hole 40 at an elevated temperature, preferably at a holding furnace, to form a passive vacuum within a center line hole 40. As shown in Figure 6B, the cutting element 60, like the upper shutter 54 described above, has an elongated portion 62 to support the cutting element 60 inside a sleeve 32, and a narrow portion 64 extending in the center line hole 40 of the porous body 38. However, different from the upper stop 54, the cutting element 60 preferably includes an elongated hollow portion 66 occupying a substantial portion of the sleeve 32. The hollow portion 66 provides additional volume to the center line hole 40 thus providing a better vacuum within The central line hole 40 followed by the diffusion of the inert gas. More preferably, however, the center line hole 40 is placed under vacuum through the inner sleeve 52 before concreting the end of the porous body 38 to a narrow portion 64 of the cutting element 60. In this embodiment, a narrow portion 64 of the cutting element 60 is measured so that the porous body 38 does not close completely on the cutting element 60 as the porous body 38 is consolidated into a concreted glass preform. Otherwise, after consolidation, the centerline orifice 40 is exposed to a reducing atmosphere by drawing vacuum through the inner sleeve 52 as the concreted glass preform is pushed down into the hot zone of the consolidation furnace. 44. The elongated portion 62 of the cutting element 60 is formed so that the inert gas within the bore of the center line 40 can pass through an elongated portion 62 of the cutting element 60 as the vacuum is pushed. As the atmosphere within the center line hole 40 is further reduced, the hot bonded glass is pushed into engagement with a narrow portion 64 of the cutting element 60, thus sealing the center line hole 40. Since the inert gas is has removed from the centerline orifice 40 by active vacuum, this embodiment of the present invention avoids the diffusion step and thus reduces all processing time. In addition, the volume provided by the elongated portion 66 of the cutting element 60 provides an added volume to the sealed centerline orifice 40, advantages of which are described in greater detail below. As described above, and otherwise in the present, the lower shutter 46, the upper shutter 54 and the cutting element 60 are preferably glass shutters having a water content of less than about 30 ppm by weight, such as fused quartz seals, and preferably less than 5 ppb by weight, such as chemically dried silica seals. Typically, said seals are dried in an atmosphere containing chlorine, but an atmosphere containing other agents for chemical drying are equally applicable. Ideally, glass shutters will have a water content of less than 1 ppb by weight. In addition, the glass shutters are preferably thin walled shutters ranging in thickness from about 200 μm to about 2 mm. Since many embodiments of the present invention depend on the diffusion of inert gas from the centerline orifice after the centerline orifice has been sealed to create a passive vacuum within the centerline orifice, the walled glass shutters thin can facilitate the rapid diffusion of inert gas from the center line hole. The thinner the shutter / cutting element, the higher the diffusion speed. After the steps described above, the concreted glass preforms can be removed from the consolidation furnace 44 and thereafter stored for further processing, preferably inside a conservation oven, or placed inside a rewinding oven where the preforms of glass can be stretched in a cylindrical glass body of reduced diameter such as a core shank, if desired. Since the concreted glass preform formed using the process illustrated in Figure 4 has a closed centerline region, and since the concreted glass preforms formed using the procedures illustrated in Figure 5A and Figure 6A have sealed centerline holes , the centerline region and the center line holes are not accessible to the atmosphere, or any environment that includes a hydrogen-containing compound. Also, the centerline region and the center line holes of the respective concreted glass preforms will remain dry during storage and / or to the rewind oven. In rewinding, the concreted glass preforms formed as described above are suspended within an oven 68 by down feed sleeves 42 as illustrated in Figures 7A, 7B, and 7C. The temperature inside the furnace 68 is raised to a temperature that is sufficient to stretch the glass preforms, preferably from about 1950 ° C to about 2100 ° C, and thus reducing the diameters of the preforms to form a cylindrical glass body as a core cane. As illustrated in Figure 7A, the concreted glass preform 70, corresponding to the porous body 38 illustrated in Figure 4 and having a closed center line region 72, is heated, preferably in an inert gas atmosphere such as He, and stretched to form a reduced diameter core rod 74 having a center line region 76 extending axially therethrough. As shown in Figure 7B, the concreted glass preform 78, corresponding to the porous body 38 illustrated in Figure 5A, is also heated and stretched to form a reduced core shank 74 having a center line region 76. However, unlike the concreted glass preform 70, the concreted glass preform 72 includes center line hole 40, which is closed to form the centerline region 76 during the rewind procedure. The reduced pressure maintained within the sealed center line hole 40, and created either actively or passively during consolidation, is generally sufficient to facilitate complete closure of the center line hole 40 during rewinding. As illustrated in Figure 7C, the concreted glass preform 80, corresponding to the porous body 38 illustrated in Figure 6A, is also heated and stretched to form a reduced diameter core shank 74 having a center line region 76. . Again, the reduced pressure maintained within the sealed center line hole 40, and created either actively or passively during consolidation, is generally sufficient to facilitate complete closure of the centerline orifice 40 during rewinding. Additional methods for closing the center line hole are described, for example in the provisional patent application of E.U.A. No. 60/131, 012, filed on April 26, 1999, entitled "Optical Fiber Having Substantially Circular Core Symmetry and Method of Manufacturing Same". Further, the closing of the center line hole 40 is improved by this method as a result of the additional volume provided to the center line hole 40 by the hollow extended portion 66 of the cutting element 60. As the volume of the center line hole 40 decreases due to at the progressive closing of the center line hole in the rewind, the extended portion 66 of the cutting element 60 provides additional volume to the center line hole 40, so that adequate volume is available to maintain sufficient vacuum within the centerline orifice 40 , thus facilitating the complete closure of the center line hole. However, preferably, as shown in Fig. 7D, before the concreted glass preform 80 reaches its softening point, a plunger 82 or other mechanism, preferably passing through the inner handle 52, can be put on. preferably in contact with the cutting element 60 to break the cutting element 60 while extracting vacuum through the inner handle 52. Once the cutting element 60 is broken, and thus open at both ends, the hole 60 center line 40 is continuously evacuated through the open ends of cutting element 60 to facilitate closing of center line hole 40 as the concreted glass preform 80 softens and stretches to form core rod 74 having a region Closed-center line 76. In a second preferred embodiment of the method of the present invention, attention is changed to avoid rewetting of the center line prior to closure of the orifice. Center line, towards the removal of water absorbed within the concrete preform glass that surrounds the center line hole due to rehumidification followed by consolidation and chemical drying. Although not critical, it is preferred that the rewetting of the preform glass surrounding the centerline orifice be kept to a minimum since it will be necessary to remove less OH and / or glass from that portion of the concreted glass preform surrounding the orifice of center line before closing the center line hole. In a method illustrated in FIG. 8, a rehumidified glass preform 84 is disposed within the upper portion of the oven 68, preferably a rewind oven, and exposed to elevated temperatures from about 1000 ° C to about 1500 ° C. While heated, the portion of the concreted glass preform 84 surrounding the center line hole 40 is treated with an agent 86 supplied from the container 88 to remove substantially all of the water (OH and / or OH2) within the region of the glass preform 84 surrounding the centerline orifice 40. Preferably, the agent 86 is a chemical drying agent such as Cl2, GeCU, SiCl4, D2, or D20 supplied from the container 88 via the supply line 90, through of the inner handle 52, and towards the center line hole 40 as a liquid, or as a gas. After chemical drying, the concreted glass preform 84 is heated to about 2000 ° C, while the center line hole 40 is placed under vacuum through the inner handle 52 to rewind the glass preform 84 into a solid core shank of reduced diameter (not shown). Alternatively, the rehumidified glass preform 84 is exposed to an agent 86 such as a chemical etching agent to remove a substantial portion of the water present residing in the portion of the rehumidified glass preform 84 surrounding the centerline hole. 40. Preferably, an acid etching chemical agent, such as but not limited to SF6, is supplied from the container 88 through the supply line 90, and internal handle 52 towards the center line hole 40 of the rehumidified glass preform. After chemical etching with chemical acid, the glass preform 84 can be heated to a temperature of about 2000 ° C while the center line hole 40 is exposed to vacuum through the inner handle 52 for rewinding the concreted glass preform 84 on a reduced diameter core rod (not shown) if desired. An additional method to the second preferred embodiment of the method of the present invention is illustrated in Figure 9. The rewetted glass preform 92 is positioned within the upper portion of the oven 68, and that portion of the glass surrounding the centerline orifice 40 is exposed to an atmosphere containing D2O. Because the deuterium diffusion characteristics in silica-containing glass are very similar to those in hydrogen, deuterium can disperse through microscopic distances in relatively short periods. When the deuterium diffuser atoms meet OH, they undergo a reversible exchange reaction with the bound hydrogen. Because the reaction is very efficient, the number of deuterium atoms does not need to greatly exceed the number of bound hydrogen atoms that reside within the glass preform 70 to achieve a substantial exchange of D / H. The D2O + OH DHOD + OD exchange reaction is obtained. After the reaction, the uncoupled hydrogen is mobile, and unless it undergoes a reverse reaction, encounters a trapping site, or becomes relatively immobile due to a decrease in preform temperature, it will diffuse out of the glass that surrounds the centerline hole 40. As illustrated in Figure 9, a gas 94, preferably an inert gas such as He, N, or Ar is supplied in a solution containing D2O 96 inside a 98 flask. The D2O conveyed by the inert gas, preferably helium, is then forced through a supply line 100 to the inner handle 52 which communicates with the center line hole 40. Preferably, the D2O is leveled through the centerline orifice. 40 for a time sufficient to facilitate the deuterium / hydrogen exchange process within the rehumidified glass preform 92. Then, the glass preform 92 can be moved to the hot zone of the glass. oven 68 and exposed to temperatures of approximately 2000 ° C.

As the glass softens, the glass preform 92 is stretched to form a reduced diameter core shank (not shown) having a closed centerline region. A large part of the OD incorporated in the glass preform 92 during the hydrogen / deuterium exchange process will be diffused by high temperature exposure in the rewind. However, any remaining OD in the resulting core rod (not shown) will contribute a little to the absorption of light in the relevant wavelength scale, since the specific absorption due to OD is about two orders of magnitude lower to that of OH in the relevant wavelength region, that is, the 1380 nm window. The reduced diameter core shank, a portion of which preferably constitutes the coating, produced by any of the above-described embodiments, may be overcoated and subsequently stretched on an optical waveguide fiber having a central core portion surrounded by a coating glass. Due to the low average weight OH content of the centerline region, the optical waveguide fiber exhibits an optical attenuation of less than about 0.35 dB / km at each wavelength within a wavelength range of approximately 1300 nm at approximately 1650 nm. In addition, the optical waveguide fiber has an optical attenuation of less than about 0.31 dB / km at a measured wavelength of 1380 nm. Figure 10 illustrates the spectral attenuation graph 102 of an optical waveguide fiber fabricated according to the invention when inserting a reduced diameter core rod or rod, made in accordance with the active vacuum mode of the present invention herein described with reference to Figure 5A, in a soot coating tube according to a soot tube bar method for fiber manufacture. As shown in Figure 10, the resulting optical waveguide fiber presents optical attenuation of less than about 0.31 dB / km at a wavelength of 1380 nm. In this way, as demonstrated by the spectral attenuation graph 104, the water peak 106 presented with an optical waveguide fiber made through a conventional manufacturing process from an OVD preform has been substantially eliminated. Although not shown in Figure 10, those skilled in the art will understand that spectral attenuation graphs similar to the spectral attenuation graph 102 can be obtained from other optical waveguide fibers incorporating a cylindrical glass body of the present invention and which are overcoated by methods other than bar-in-tube. As shown in Figure 11, and according to another embodiment of the present invention, an optical fiber 108 manufactured in accordance with the present invention can be part of a fiber optic communication system 110. The fiber optic communication system 110 generally includes a transmitter 112, a receiver 114, an optical waveguide fiber 108 for communicating an optical signal between the transmitter 112 and receiver 114. Within the optical fiber communication system 110, the optical waveguide fiber 108 it has an optical attenuation of less than about 0.31 dB / km at a measured wavelength of 1380 nm.

EXAMPLES The invention will be further elucidated by the following examples, which are intended to illustrate the invention. For each example set forth below, it will be understood that the distances are described measured from the top of the furnace muffle. 10 EXAMPLE 1 A one-meter soot preform, formed by an OVD procedure and equipped with a chemically sealed tip Dry placed within the lower portion of the centerline hole, was loaded in the upper portion of a consolidation furnace maintained at a temperature of about 1000 ° C-1200 ° C to a depth of about 1090 mm. Prior to loading, a chemically dried solid top seal measuring approximately 15.5 cm 20 long inside the center line hole in the upper part of the preform. The preform was initially prepurged for approximately 15 minutes with a flow rate of 20 SLPM He in the muffle and flow rate of 1.5 SLPM He along the center line hole. The purge was followed by a aÉ flt¡n ^ Haai * fe- drying step of 240 minutes. During the drying step, a flow velocity of approximately 0.825 SLPM Cl2 and 20 SLPM He was passed through the muffle. Then, the preform advanced down 1090 mm to a depth of approximately 2730 mm in the hot zone of the furnace at a speed of approximately 5 mm / min. under a He flow rate of 20 SLPM inside the muffle. At a depth of approximately 2510 mm, a Cl2 flow of 300 SCCM was supplied through the center line hole of the preform until it reached a depth of approximately 2540 mm, at which time the central line flow of the preform was determined. Cl2. At that depth, and with the termination of the centerline flow, a vacuum pump was activated which communicates with the centerline to reduce the pressure within the centerline hole. Vacuum was continued to be drawn until the bottom of the preform reached a depth of 2730 mm and the top portion of the preform was closed in the top plug, thus sealing the center line hole. The sealed concrete preform was stretched on a solid shank in a rewind oven as a result of the reduced pressure contained within the sealed center line hole. The cane was overcoated using the bar method in soot tube, and the overcoated cane was chemically dried, consolidated, and then stretched in an optical fiber, which presented the following optical attenuation: Attenuation results 1310 nm 1380 nm 1550 nm CUTTING FIBER DIAMETER 0. 336 dB / km 0.301 dB / km 0.245 dB / km 1258 nm 130 μm EXAMPLE 2 A one-meter soot preform, formed through an OVD process and equipped with a chemically dry tip plug placed within the bottom of the center line hole, was loaded into the upper portion of a consolidation furnace maintained at a temperature of approximately 1000 ° C-1200 ° C to a depth of approximately 1090 mm. Prior to loading, a chemically dried solid top seal measuring approximately 17.0 cm in length was disposed within the center line hole in the top of the preform. The preform was initially prepurged for approximately 15 minutes with a flow rate of 60 SLPM He in the muffle. This was followed by a 60 minute drying step. During the drying step, flow velocity of 0.825 SLPM of Cl2 and flow velocity of 20 SLPM of He flowed through the muffle. The drying step was then followed by another purge step at a flow rate of 60 SLPM He for the flask for 15 minutes. The muffle gas was then changed to deuterium oxide (D2O) for 60 minutes, thus exposing the preform, and thus the center line hole, to D2O. During this time, the deuterium oxide bubbler was maintained at 82 ° C while a He SL flow rate of 1.9 SLPM passed through the D2O inside the bubbler as a carrier gas. In addition, there were 18 SLPM of He flowing through the muffle. After the preform was exposed to deuterium oxide for about 60 minutes, the preform was purged again for 15 minutes under 60 SLPM He flow in the flask. A final drying step was performed where an IC2 flow rate of 0.825 SLPM and a He SL flow rate of 20 SLPM were supplied to the flask for approximately 180 minutes. After the drying step, the preform 10 advanced downward toward the hot zone of the 1090 mm furnace at a depth of 2730 mm at a speed of 5 mm / min. while a He flow rate of 20 SLPM passed through the muffle. When the bottom of the preform reached a depth of 2435 mm, a vacuum pump was activated that communicates with the center line hole for 15 reduce the pressure inside the centerline hole. The vacuum continued to be removed until the bottom of the preform reached a depth of 2630 mm and the top portion of the preform was closed in the top plug, thus sealing the center line hole. The sealed concrete preform was then stretched on a solid shank in an oven 20 rewinding as a result of the reduced pressure contained within the sealed center line hole. The cane was overcoated using the bar method in soot tube, and the overcoated cane was chemically dried, It was consolidated, and then stretched on an optical fiber, which presented the following optical attenuation: Attenuation results 5 131 Onm 1380nm 1550nm FIBER DIAMETER CUT 0.379 dB km 0.328 dB / km 0.242 dB / m 1300 nm 120 μm EXAMPLE 3 A soot preform of one meter, formed by an OVD process and equipped with a chemically dry tip seal placed within the lower part of the center line hole, was loaded into the upper portion of a consolidation furnace maintained at a temperature of about 1000 ° C-1200 ° C to a depth of about 1090 mm. Prior to loading, a chemically dried solid top plug (cutting element) was disposed within the central hole in the upper part of the preform. The preform was initially prepurged for approximately 15 minutes with a flow rate 20 of 20 SLPM He in the muffle and flow rate of 1.5 SLPM He along the center line hole. The purge was followed by a drying step of 240 minutes. During the drying step, a flow velocity of approximately 0.825 SLP Cl2 and 20 SLPM He was passed through the muffle. ^ u ^ -ÜÉdan ^ a ^ * »- _ ^ __ ^ | _ ^ __ ^^^^ ___ aa_a _ ^ _ ^^^^ _ ^^^^^^ _ ^ aafcWB1tMkÍ Then, the preform advanced downward 1090 mm at a depth of about 2675 mm inside the hot zone of the furnace at a speed of about 5 mm / min. under a He flow rate of 20 SLPM inside the muffle. When the bottom of the preform 5 reached a depth of approximately 2675 mm, a vacuum pump was activated which communicates with the center line to reduce the pressure within the center line hole. Vacuum was continued to be drawn for approximately 40 minutes, at which time the upper portion of the preform closed the top shutter, thus sealing the center line hole.

The sealed concrete preform was then placed inside a rewind furnace under an argon muffle and purged from the centerline. A plunger was then lowered through the internal handle to break the cutting element, the cutaway argon purge was completed at the cuat, and a vacuum pump was coupled to draw vacuum through the centerline and 15 evacuate the center line hole. The orifice of the center line of the concreted preform was closed under active vacuum during rewinding to form a reed. The resulting cane was overcoated using the bar method in soot tube, and the overcoated cane was chemically dried, consolidated, and then stretched in optical fibers, which presented the following 20 optical attenuation: "He was there.

Attenuation results 1310nm 1380nm 1550nm CUTTING FIBER DIAMETER 0.338 dB / km 0.297 dB / km 0.220 dB / m 1168 nm 115 μm 0.337 dB / km 0.301 dB / km 0.20 dB / km 1209 nm 125 μm It will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the spirit and scope thereof. For example, the centerline orifice can be sealed by flame-treating the glass preform formed towards the top shutter in the centerline hole after or while the concreted glass preform is removed from the consolidation furnace under vacuum. Preferably, the concreted glass preform is removed from the consolidation oven while an inert gas, free of hydrogen-containing compounds, flows between the descent handle and internal handle to prevent water from entering the center line hole between the joint formed by the handle of preform and the internal handle. Once the center line hole is closed by a flame torch, the flow of inert gas can be terminated. Thus, it is intended that the present invention encompass the modifications and variations of this invention as long as they fall within the scope of the appended claims and their equivalents.

Claims

NOVELTY OF THE INVENTION CLAIMS 1. A method for manufacturing a cylindrical glass body for use in fiber optic guide fiber fabrication, characterized in that it comprises the steps of: a) chemically reacting at least some of the constituents of a moving fluid mixture comprising at least one glass forming precursor compound and an oxidizing medium, the reaction resulting in the formation of a silica-based reaction product; b) depositing at least a portion of said reaction product on a substrate to form therein a porous body, at least a portion of said porous body including hydrogen bound to oxygen; c) removing the substrate from said porous body, thereby forming a central line hole extending axially through said porous body; d) consolidating and drying at least a portion of said porous layer to form a glass preform; e) closing the center line orifice and said drying, consolidating and closing steps are performed under suitable conditions to result in a solid glass body suitable for making an optical fiber having an optical attenuation of less than about 0.35 dB / km at a wavelh of 1380 nm. 2. The method according to claim 1, further characterized in that said closing step results in a solid glass body suitable for making an optical fiber having an optical attenuation of less than about 0.31 dB / km at a lh of 1380 nm wave. 3. The method according to claim 1, further characterized in that it comprises the step of replacing at least a portion of the hydrogen bound to oxygen with deuterium in a deuterium / hydrogen exchange step carried out after step c). 4. The method according to claim 3, further characterized in that said deuterium / hydrogen exchange step comprises supplying D20 in the center line orifice. 5. The method according to claim 2, further characterized in that the step of consolidation and drying comprises chemically drying said porous body inside a consolidating furnace to reduce the concentration of average OH in weight within said porous body to less than about 1 ppb, and wherein said closing step is carried out during the consolidation and drying step. 6. The method according to claim 1, further characterized in that said closing step comprises preventing at least the central line hole from being exposed to an atmosphere comprising a hydrogen-containing compound subsequent to step d). 7. The method according to claim 6, further characterized in that said step of prevention comprises the step of creating a vacuum within the center line hole. 8. - The method according to claim 7, further characterized in that said step of prevention comprises placing a shutter in the center line hole at each end of said porous body, and heating said porous body in an atmosphere of inert gas at a sufficient temperature to concretize each end of said porous body towards said obturators, thus sealing the central line orifice. 9. The method according to claim 8, further characterized in that said step of prevention comprises placing a chemically dried glass stopper in the center line hole at each end of said porous body, the chemically dried glass shutter having a content of OH of less than about 1 ppb in weight. 10. The method according to claim 8, further characterized in that said prevention step comprises heating said porous core to disperse the inert gas from the sealed central line hole. 11 - The method according to claim 10, further characterized in that said closing step comprises the steps of: placing said glass in an oven; heating said glass body inside said furnace; and stretching said glass cavity in a reed having an outer diameter less than the outer diameter of said glass body. 12. The method according to claim 8, further characterized in that said prevention step further comprises exposing the center line orifice to an atmosphere that reduces pressure through at least one end of said porous body during said heating step. . 13. The method according to claim 12, further characterized in that at least one of said shutters is susceptible to rupture, and wherein said closing step comprises the steps of: placing said glass in an oven; break said shutter; exposing the centerline orifice to an atmosphere that reduces pressure; heating said preform during said exposure step; and stretching said glass body in a reed having an outer diameter lower than the outer diameter of said glass body. 14. The method according to claim 1, further characterized in that said method comprises purging said central line chamber with a drying gas comprising a compound 15 selected from the group consisting of: CI2, GeGU, SiCI4, D2 and D2O subsequent to step d). 15. The method according to claim 1, further characterized in that said method comprises the step of chemically etching at least a portion of the gas line surrounding the central line hole before step e). 16. A cylindrical glass body for use in the manufacture of optical waveguide fiber made through the method claimed in claim 1. ? **** 44? ?? * 17. - A cylindrical glass body for use in the manufacture of optical waveguide fiber characterized in that it comprises: a glass containing silica, at least a portion of which includes hydrogen bound to oxygen, said glass containing silica having a region of center line formed by closing a center line hole of a preform, said glass containing silica having a sufficiently low weight average OH content such that an optical waveguide fiber made from said cylindrical glass core has a Optical attenuation of less than about 0.31 dB / km at a wavelength of approximately 1380 nm. 18. The cylindrical glass core according to claim 17, further characterized in that the average OH content by weight is less than about 1 ppb. 19. An optical waveguide fiber characterized in that it comprises: a core glass containing silica, at least a portion of which includes hydrogen bound to oxygen, said core glass containing silica having a central line region that includes a dopant, the centerline region being formed by closing a center line hole of a preform; and a coating glass surrounding said silica-containing core glass, further characterized in that said optical waveguide fiber has an optical attenuation of less than about 0.31 dB / km at a wavelength of about 1380 nm. 20. - The optical waveguide fiber according to claim 19, further characterized in that said core glass containing silica includes a weight average OH content of less than 1 ppb. 21. The optical waveguide fiber according to claim 19, further characterized in that said fiber has an optical attenuation of less than about 0.35 dB / km at each wavelength within a wavelength scale of about 1300 nm at approximately 1680 nm. 22. The optical waveguide fiber according to claim 19, further characterized in that the dopant comprises germanium dioxide. 23. The optical waveguide fiber according to claim 19, further characterized in that said coating glass comprises silica. 24. A fiber optic communication system characterized in that it comprises: a transmitter; a receiver; and the optical fiber claimed in claim 19 for communicating an optical signal between said transmitter and said receiver. 25. A shutter for use in sealing the center line hole of a soot preform used in the manufacture of an optical waveguide fiber, characterized in that it comprises: a glass containing silica, at least a portion of which it comprises hydrogen bound to oxygen, said glass containing silica having an OH content of less than about 5 ppm by weight. 26. The obturator according to claim 25, further characterized in that said silica-containing glass comprises an OH content of less than about 1 ppb by weight. 27. The obturator according to claim 25, further characterized in that said silica-containing glass comprises a prolonged body having an open end and a closed end, said prolonged spout defining a chamber having a volume. 28.- The shutter in accordance with claim 25, further characterized in that said extended body has a thickness of less than about 2 mm. 29. The obturator according to claim 25, further characterized in that said extended body has a thickness of between about 200 μm to about 2 mm. A method for manufacturing a cylindrical glass body for use in fiber optic guide fiber fabrication, characterized in that it comprises the steps of: a) chemically reacting at least some of the constituents of a fluid mixture in motion comprising at least one glass forming precursor compound and an oxidizing medium, the reaction resulting in the formation of a silica-based reaction product; b) depositing at least a portion of said reaction product on a substrate to form therein a porous body, at least a portion of said porous body including hydrogen bound to oxygen; c) removing the substrate from said porous body, thus forming a central line hole extending axially through said porous body; c) consolidating and drying at least a portion of said porous layer to form a glass preform; and e) closing the central line orifice and said drying, consolidating and closing steps are performed under suitable conditions to result in a solid glass body including a center line region having a weight average OH content of less than approximately 1 ppb.